Zinc phosphate material and method of making same



Patented Sept. 12 1933 i t o zI No who sP-nA'rE- ,MATaRiAL Miiirfioi) V meirzeseerperetion er Michigan r V Serial-No. 5143123;

- s cretar at (c1. 23-1 05) 1 Y Na -Drawings Atheists reti'sery 1,? her This applicatidh' relates'toa zine'iphosphat'e the-crystals-mayb e 'fairly well dried in the material arid aFmethod of making the same. 'centri-fugee It-is then ready-to packs The'purp'o'se ofthe 'invehtion is toproyide a zinc The 'remairiingmother' liquormay; then be Dhospha'te' ihatterial whichis uniformdncompo used-11 i: forming a new.; s olu tion,'suificientacid 5 sitionand is composedof separate'srnall crystals and Zinc being added to bring the proportions 6,0

forming a granular 'mass easily -handled"and Zinc and 50% t0 5 %*ph QDhQ acid, suffie'ie'ritlystabl for cornmercial purposes; When-the Zinc isdissoIVed. The strength of Tha -material ma be"'used"-to form and/orphosphoric acid which is; added to bring this py g i ru'g p ofing"solutionsy'or to form 'a I'BSHIt YaIlES with the evaporation of the water platingsolutionfor for'other purposes. It may oeeu f "duringtheproceee, i i orp it 65* be' readil-y shippedwhe're'itis needed for use, isfoundthat ='-75% ac-id may be used with only and 're'rn'aihs' in an easily divisible and readily Occasional-correction to securethe right consolubleform and of substantial-lyconstantc'omif n of the resultant solution. position." r A'solution may be made richer than:

15' The material is composed of zinci'phosphate Zine, pecially lithe-concentration -offacid at 70 crystalsei the' orthorhombic form and having a he completion of' solut ion. is. allowed: to run chemical composition corresponding closely with down; u the TTeSulti'Ilg Cry tallization is hard the formula Zn (H2PO4)22H2O, or, expressed in to control a rm a productvwhich is manother way, substantially ZnO 27.5%, P205 cult'to handle satisfactorily in the centrifuge, 48.1%, H2O 24.4%. While the size of the crystals If. m t i o zinc is d ss v d, it ha 75 may vary somewhat, as will appear later, the been found alIIlOSt impossible. to p a a y preferred material is composed of crystals the Stalline p the result being akind of p great, majority of which are'between 1 mesh which retains much of the acid'not utilized in and 30 mesh. Smaller crystals are moreapt to dissolving h V absorb moisture and t Cake, while larger crys- Treatment, otherwise as described, of a solu- 80 tals are less quickly soluble; tion containing 14% zinc, results in crystalliza- The preferred method of making this 'material tionybut the crystals are so small that they canwill be described, and then some possible varianot be readily Separated from the r liquor tions of the method will be indicated. i in a t u e. p I A solution of zinc and phosphoric acid is H e d ssol t p e be formed, the dissolving being completed with the if desired, u are e a y and merely Waste solution at a temperature of about C. to heat and lifelong the Cooling P od- G. Since dissolving zinc in a solution of' phos- If ap d oo ng iscontinued below 45 C. to phorie acid results in considerable foaming, it crystallization, '01 if cooling is continued after I is best to feed the zinc into the solution someyetal sw under y, the P p e what slowly. The supply of zinc is stoppedwhen forms s a of the triehnie yp y fi ea d the zinc constitutes about 15% of the solution. mostly Short, so a pasty mess resultsdiffi- When the zinc is all dissolved, the solution con- Cult to Separate in a Centrifuge and much more tains between 50% and 55% of phosphoric acid. hygroscopic than the orthorhombic crystals 5? f The solution formed as described is cooled E g be sepilmted i mm as a ry, gran ar mass, an even 1 dried 28:13, 1 gt zi zg gg gfi gg g i g fi? initially, quickly absorbs water from the atmostinued slowly (it may be at the rate of 4 C. per phere 1mm It Is pasty 45 hour) until the first signs of crystallization appear, which Occurs at a temperature of from herent crystals from which the 'mother liquor Thereupon cooling is Stopped cannot be separated readily, and. which cannot at Once and, as h erystallization Proceeds, be handled or dissolved as readilyfias the product the heat of crystallization warms the solution e lting from the described process. .The'pow Failure to stir duringthe crystallization, or too high zinc'content, results in, masses of co- 5o3ib011t before the Process is pl ddery or granular material described is prefer- The solution is ontinual y stirred during the able to a paste becauseit is easier to handle,

crystallizing period. As soon as the temperature easier to dissolve, is much more uniform as to' becomes constant, or tends to'drop, the'solution composition, and contains the materials in about is again cooled for centrifuging. The solution, the proportions desired for rust-proofing and "prepared in this way, may be piped readily, and for plating purposes. It is fairly. stable up to terial has been described with considerable eX- actness, and any'considerable variations are un' 2 its melting point of C., well above normal atmospheric temperature. Paste is likely to become liquid at a lower temperature, altho the actual melting point of the orthorhombic and triclinic crystals appears to be. essentially the same. r o

While 15% zinc in the solution is preferred for reasons stated, a variation of little over 14% zinc with about 60% free acid to a little under Y tals which comprises forming a hot aqueous 17% zinc with about 42% free acid can be used with some success. When desired, a small amount of a material such as boric acid may be, added to assist in retaining the crystals in their separate form, and other chemicals may be added in small amounts to modify the resultant bath, but the essential feature of the new material is the zinc phosphate of the composition and of the form and condition of crystal described.

The preferred method of'producing the madesirable for reasons stated, but some changes may be made within the scope of the appended claims.-; I

What I claim is:

1. A material-consisting essentially of separate orthorhombic crystals having a composition found by quantitative analysis to be substanman 27 /270 ZnO, 48% P205 and"21/z% H2O.

- 2. A material consisting essentially of separate orthorhombic crystals the great majority of which are of a size between lfimesh'and 30 mesh and which have a composition: corresponding closely to the formula 'zmHzPOi) 221-120.

' 3. The method ofmaking zinc phosphate crys- 7 ing the process.

tals which comprises forming a hot aqueous 'solutionof zinc and phosphoric acid containing more than 14% and less than 17% zinc and from 42% to 60% acid when the zinc is dissolved,

cooling the solution untilcrystallization begins,

then stopping the cooling and stirring the solut'ion during crystallization, and separating the resultant crystals from the mother liquor.

4. The method of making zinc phosphate cryssolution' of zinc and phosphoric acid containing about 15% zinc and 50% to 55% free phosphoric acid, cooling the solution until crystallization starts, "immediately stopping the cooling when crystallization starts and stirring during crystallization, and separating the resultant crystals from the mother liquor.

5. The method of making zinc phosphate crystals which comprises forming a hot aqueous solution containing about 15% zinc and between 50% land 55%, phosphoric after reaction between the .zinc and phosphoric acid is-complete, cooling the solution rapidly to about.45 C. continuing the cooling thereafter at a rate of the order of 4 C. per hour, until crystallization begins at from 32 C. to 34:? (3;, then stopping the cooling and allowing the heat of crystallization to raise the temperature of the solution,

stirring the solution during crystallization, after the temperature of the solution becomes stationary cooling once more and centrifuging, heatingrthe mother liquor and adding; thereto sufficient zinc, phosphoric and water to restore it to the proportions indicated above, and repeat- VAN M- 'DARSEY. 

